Slurry was collected from two groups of finishing pigs
fed either a standard commercial diet
(containing 205 g/kg crude protein (CP)) or a specially
formulated lower CP content diet (140 g/kg
CP). The slurries were surface applied to grass/clover
plots on a freely draining soil in SW England
in mid-March 1995 at three application rates: 25, 50 and
70 m3/ha. Measurements were made from
the 50 m3/ha plots of ammonia volatilization,
denitrification, nitrous oxide and methane emissions
and nitrate leaching. Measurements of herbage yield and
apparent N recovery (ANR) were made
from all plots. Decreasing the CP content of the pigs'
diet reduced N excretion by the pigs and also
changed other characteristics of the slurry. Slurry from
pigs fed the lower CP diet (the slurry referred
to hereafter as LS) had a higher dry matter (DM) content,
lower pH, lower total ammoniacal N
(TAN), total N and VFA content with a similar total C content
compared with slurry from pigs fed
the standard commercial diet (the slurry hereafter referred
to as CS). From the 50 m3/ha treated
plots, losses by ammonia volatilization represented 38 and
58% of the applied TAN and net losses
through denitrification represented 5·3 and
12% of the applied TAN for LS and CS respectively.
Nitrous oxide emission was similar from the two slurries, with
net emissions of c. 0·5% of the applied
TAN. Methane emission was significantly less from LS. No
nitrate leaching was detected either in
spring or in the following autumn. Yield and ANR increased
with increasing slurry application rate
up to 50 m3/ha. The best% N recovery was from
the 50 m3/ha application rate with 58 and 47% of
the applied TAN being recovered from LS- and CS-treated plots
respectively. Changes in the slurry
characteristics due to the lower CP diet resulted in lower
losses to the environment and an improved
utilization of the slurry N by the herbage.